Rock drilling apparatuses can be used within a number of fields of application. For example, rock drilling apparatuses can be used in tunnel driving, underground mining and rock reinforcement, in which the drilling, for example, can constitute drilling of blasting holes, injection holes, holes for the insertion of rock bolts, etc.
Depending on the type of field of application and/or type of drilling, drilling can take place under widely varying types of conditions, in which different drilling conditions typically pose different types of problems. In underground mining, for example, rock can be mined in different drilling directions, such as upwards, downwards and/or horizontally, in which drilling in the respective different directions can give rise to different types of problems. For example, the working height, i.e. the distance between the roof and floor of the mine, can be limited, with associated problems when drilling upwards or downwards.
In the case of downwardly directed drilling, further problems often arise. In the mining of an ore body or in tunnel driving, for example, a number of holes are usually drilled within a limited area, after which, when drilling of all the holes within the desired area has been completed, the holes are loaded with explosives for subsequent mining.
In the course of the drilling, drilling residues, so called drill cuttings, are formed and these drill cuttings are evacuated from the hole while drilling is in progress. This is usually carried out with the aid of a flushing medium, such as, for example, compressed air, flush air, which is led through a channel in the drill string for discharge through flush air holes in the bit so as thereafter to take the drilling residues with it on its way up out of the hole. In underground drilling, the flushing medium is usual constituted to a certain degree by a liquid such as, for example, water, for binding the drill cuttings and reducing dust formation.
When a number of holes are drilled close together in a downwardly directed manner, the problem arises, however, that the drill cuttings which are formed in the drilling of a hole are at risk of running down into already drilled holes in the vicinity of the hole which is currently being drilled, which leads to subsequent work with cleaning of already drilled holes. According to the above, moreover, a flushing medium at least partially consisting of liquid is usually used in underground drilling, which means that the drill cuttings form a clay paste, which after a number of drilled holes can cover the whole of the drilled surface, with the result that drilled holes, apart from being awkward to clean from drilling residues, can also be difficult to find.
For this reason, a first part of the hole is usually drilled first, after which the drill string, consisting of one or more drill rods, is pulled out of the hole and a pipe is inserted into the upper part of the hole before the hole is finish-drilled to the desired depth. This pipe insertion is laborious, however, and often requires the hole to be cleaned from cuttings before the pipe is inserted. Furthermore, once the pipe is in place, surrounding holes must be filled so that the pipe stands firm. During filling around the pipe, it is also easy for the angle of the pipe to be altered. Furthermore, it can be difficult to get the pipe down, in which case a feed device, for example, can be used as a power source to press down the pipe, with the risk of damages both to the pipe and to the feed device.
There is thus a need for an improved drilling method, primarily for use in, but not limited to, downwardly directed drilling underground.